Disk drive devices using various kinds of media, such as optical disks, magneto-optical disks, flexible magnetic disks, and the like have been known in the art. In particular, hard disk drives (HDDs) have been widely used as storage devices of computers and have been one of the indispensable storage devices for current computer systems. Moreover, HDDs have found widespread application to moving image recording/reproducing apparatuses, car navigation systems, cellular phones, and the like, in addition to the computers, due to their outstanding characteristics.
A magnetic disk used in an HDD has multiple concentric data tracks and servo tracks. Each servo track contains multiple servo data having address information and each data track includes multiple data sectors containing user data recorded thereon. Data sectors are recorded between servo data discrete in the circumferential direction. A head element portion of a head slider supported by a swinging actuator accesses a desired data sector in accordance with address information in the servo data to write data to and retrieve data from a data sector.
In order to increase the storage capacity of an HDD or to improve the reliability of an HDD, it has been proposed to determine a data track pitch for each head (each recording surface). Determination of the data track pitch so as to match head characteristics such as a read width or a write width leads to suppression of adjacent track interference (ATI) in data write and increase in data capacity per recording surface.
Two approaches have been proposed to adjust the data track pitch for each recording surface. One is a method to make servo tracks conform to data tracks and adjust the servo track pitch for each recording surface in the servo track write (refer to Japanese Patent Publication No. 2006-114142 “Patent Document 1”, for example). The other is a method to provide servo tracks with a common pitch to all recording surfaces and adjust the data track pitch for each recording surface.
In order to improve performance, a technique has been proposed that performs a head switch for every data track in sequential data write or data read. However, if the recording surfaces have different data track pitches, the head switch for every data track leads to degradation in performance. If the recording surfaces have different data track pitches, their respective data tracks show different radial positions even if their data track numbers are the same. Accordingly, a transition onto the same data track on another recording surface requires additional time for a head seek. To avoid the additional seek, a data track of close radial position must be found on the recording surface of the transition destination in every head switch. To this end, additional resources and time are required for this operation.
An effective approach to overcome this problem is a data track format in which a recording surface is constituted by multiple bands. Each band is constituted by multiple consecutive data tracks. Upon completion of an access to one data track, the HDD selects an adjacent data track in the same band as the next data track and switches heads at an end of the band. This reduces the number of head switches and suppresses increase in additional process time due to the head switches.
In the above data track format, the switch destination in a head switch is a data track at a band end on another corresponding recording surface. Each recording surface has the same number of bands; each band on a recording surface has the same number of data tracks, too. Specifically, a resulting value of dividing the number of data tracks on a recording surface by the predetermined number of bands is set to the number of data tracks in each band.
If the recording surfaces have invariable data track pitches, or if they have the same variation rate of the data track pitch in the radial direction, the radial positions of band ends are aligned as shown in FIG. 9(a). In the example of FIG. 9(a), all recording surfaces corresponding to four heads are divided into 1,500 bands each. The squares represent bands and the number in each square represents the number of data tracks in the band. On each recording surface, the number of data tracks in a band is invariable. Among the recording surfaces, the number of data tracks in a band on a recording surface is different from the one on another recording surface. If the variation rates of the data track pitches in the radial direction are the same, the radial positions of the band ends align with each other even if the recording surfaces have different total number of data tracks. Accordingly, the HDD can access the target data track quickly in a head switch.
On the other hand, if the recording surfaces (heads) have different variation rates of the data track pitch in the radial direction, the radial positions at the band ends do not align among the recording surfaces. FIG. 10 shows an example of measurements of the magnetic core width (MCW), i.e., the magnetic write width of each head with respect to the radial direction. The X axis represents servo tracks, and the Y axis represents the data width in writing the servo track in the unit of PES. It will be understood that the variation rates of the data track pitches significantly differ depending on the head. In this way, if the variation rates of the data track pitches are significantly different depending on the head, the differences between the band ends in the radial position become large among the recording surfaces so that efficient head switches cannot be performed. Therefore, an HDD having different increasing or decreasing rates of the data track pitch in each head requires a data track format which can accommodate the differences in head characteristics and achieves efficient head switches.